Poly(α-methyl styrene) polymer additive for organic thin film transistors

While great progress has been achieved in the research of various solution-processed organic semiconductors, the randomized crystal orientations and charge carrier mobility variations have posed tremendous challenges to implement the organic semiconductors for organic electronic device applications. Among the miscellaneous polymer additives reported to tune the crystal growth and modulate charge transport, poly(α-methyl styrene) (PαMS) has been extensively studied for its capability to improve semiconductor crystallization, reduce bulk crystal misorientation, induce phase segregation, enhance morphological uniformity and boost electrical performance of organic thin film transistors and organic electronic devices. In the first section of this article, we review the recent progress of organic electronics and highlight the crystal misorientation and mobility variation as the challenges that need to be overcome. Then, the various merits from mixing polymeric additives with organic semiconductors are discussed. In the second section, we provide an overview of the previous works that employ PαMS for regulating the crystal orientation alignment and modulating charge transport of miscellaneous solution-processed small-molecular organic semiconductors including 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) and 2,8-difluoro-5,11-bis(triethylsilylethynyl)anthradithiophene (diF-TESADT). By discussing these important examples, we intend to demonstrate that PαMS can be versatilely implemented to improve other new organic semiconductor crystallization and mobility for high-performance organic electronic applications.

     

Poly(butyl acrylate) polymer enhanced phase segregation and morphology of organic semiconductor for solution-processed thin film transistors

The phase segregation as a result of mixing organic semiconductors with polymeric additives has been reported as an intriguing avenue to optimize semiconductor crystal microstructure, active layer composition and charge carrier transport. In this work, we report the mixing of organic semiconductor 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) with poly(butylacrylate) as a polymer additive to control the semiconductor crystal growth and morphology. The incorporation of poly(butylacrylate) induces a vertical phase segregation but a more predominant lateral phase segregation with TIPS pentacene. Along with a solvent vapor annealing technique, poly(butylacrylate) evenly distributes the semiconductor nuclei on the polymer matrix, and results in organic crystal with enlarged grain width. In addition, the randomized crystal growth of TIPS pentacene has been significantly reduced, giving rise to a 25-fold decrease in misorientation angle. The bottom-gate, top-contact thin film transistors with the poly(butylacrylate)/TIPS pentacene mixture as the active layer demonstrated an improved hole mobility of 0.11 cm²/Vs. We believe the phase segregation induced by the poly(butylacrylate) polymer as well as the solvent vapor annealing method as reported in this work can be facilely replicated on other organic semiconductors to realize high performance organic electronic device applications.